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1y ago

Owl-natomy: Feet and Talons (huge post, tons of pics and info!)

A request by @verdeviento@mander.xyz for some more info on talons.

Owls are a type of raptor. The origin of the word raptor comes from the Latin word rapere, which means “to seize.” That is because for a raptor, their feet are key to their survival. They catch their food, they’re used for grooming, and they’re the main line of defense.

Basic Anatomy

There are many differences in owl leg and foot anatomy when compared to other birds.

Owl foot and leg bones are shorter and thicker than other birds. This allows for a thicker muscular structure, even greater than that of most eagles many times greater in size. This sturdiness also helps the feet and legs withstand impacting their prey at high speed.

A is a hawk leg bone, B is an owl leg bone

Another advantage owls over other raptors is calcification of the leg tendons. This hardening occurs in areas of high stress. It allows more structural support in areas that need it and serves as a calcium reserve should a bone injury occur. These structures are called sesamoids.

Owl tendons are also arranged in a way that they are tensed when the bird is relaxed. This is the opposite of how our hands work. To grip tighter, we need to exert more and more force, but the owl just has to use energy to release its grip. This allows them to exert maximum force holding onto prey with minimal effort. It is also what lets them stay gripped to their perch when they sleep without falling off. They must consciously let go to relax their grip.

This article has some good animations on the way the tendons lock up the grip. Animated gifs work for me on Boost, but not Liftoff so I'll just put the link here so I know everyone can look at it.

Owls are zygodactyl, meaning they have toes that are arranged in a 2 rear facing / 2 front facing, as opposed to most birds which are anisodactyl, with a 3 rear facing / 1 front facing arrangement. Owl toes are also of equal length, as opposed to having one longer toe in front. Owls do have the ability to move their fourth toe to either the front or back to allow force to be distributed in different ways.

Typical bird foot

Owl 2 by 2 grip

At the end of their toes are the talons. Owl talons are made of keratin, just like our fingernails. They have a hard outer layer and a soft inner layer, which makes them very hard, but also maintain some flexibility.

Inner and outer talon layers

Owl talons vary in size by species, but they are relatively long compared to their toe size. This increases the leverage in can apply. The Eurasian Eagle Owl has talons that can be up to 4 inches / 10 cm long.

Eurasian Eagle Owl feet

Grooming

Preening is an important part in owl grooming as it maintains the integrity of their feathers. Owls use their feet to arrange feathers, remove debris and parasites, and spread oils throughout the feathers.

Most birds have a ridge on their talons that aid in this, but the Barn Owls have evolved serrations that look and act like a comb.

Barn Owl talon

Another view

Hunting

Why do owls hunt with their feet and not their beaks? Owls have short and rather weak beaks. The tip is curved and can generate a good amount of tearing force, but it is not good for offense or defense. By using the feet, they not only have much great mechanical advantage, they also keep any danger as far from their face as possible. Owl eyes and ears are their means of locating food, so they need to keep them protected.

Owls will swoop down on prey with their talons spread to allow the maximum grabbing area possible. Many hunt at night and cant actually see their prey, so this increases the odds of being on target. The 2 by 2 toe arrangement allows maximum gripping force to be evenly distributed. With the toe that can move from back to front, they can adjust their grip if they somewhat miss their mark. The undersides of the feet are also highly textured to add additional grippiness. The feet are also covered with many sensory nerves to detect vibrations in the air or on the ground, so that also helps them “see” without being able to see.

Splayed talons to increase grabbing area

Grippy surface of foot

Once they have their grip on their prey, they do not use their talons to kill like hawks or eagles do. All the combined mechanical advantage of their bones and tendons is used like a hydraulic press to finish off their prey. Most eagles and hawks have much less grip strength because they do use their talons to kill. A Bald Eagle only has half the grip strength of a Great Horned Owl, even though the eagle is much larger.

Owl grip strength is not to be overlooked. The Great Horned Owl is one of the strongest birds, with a grip strength approaching 500 psi / 3450 kPa. An adult human can grip around 150 psi / 1025 kPa. A pitbull bite is less than 250 psi / 1700 kPa, and only when we reach dogs the size of an English Mastiff do we reach dogs large enough to generate as much gripping force as a Great Horned Owl. To compare sizes, an adult Mastiff is over 200 pounds / 90 kg, where a GHO weighs 3 pounds / 1.4 kg.

GHO vs Mastiff size comparison

82 comments

Forgot to add my sources! Here's where most of this info came from.
Quora discussion from Raptor handler
Atlantic article
AviBirds.com
Owl Pages
Random Fun Facts
UMN Raptor Center
- Awesome post! Very informative and concise.
  
  Thank you! It was hard picking what to leave out. Much of this anatomy had been studied in great detail since it's the most unique characteristic of raptors. Many people have written long scientific studies on just each individual fact I included with all kinds of pictures and radiolicic images of bones and fancy statistics. This isn't my career though, so this was enough work for me! 😉
- Great post! I appreciate all of your effort!
  
  Glad you liked it! I knew it would be a long post because there are so many parts working together to make the system as amazing as it is. I couldn't just talk about one or 2 things since it would just make more questions, so I tried to cover all the basics.

This was a very interesting read, thank you.
- I am glad you liked it! This post was a lot of effort and I'm glad Lemmy didn't screw it up while I was making the post itself, and I also got to learn a lot while making it.

I would like to subscribe to owl facts
- I would like you to subscribe!
  I got a good owl coming up for tomorrow. I see lots of posts about it other places, but they all miss the best thing about it!

This is one of the best posts on lemmy I've seen yet. Thanks for the great write up.
I had no idea that they were a kind of raptor. Nor how strong they are.
- I had no idea that they were a kind of raptor. Nor how strong they are.
  They are masters of surprise after all!
  I'm very grateful you've all enjoyed this. I enjoy finding these things for you all, and I'm glad this community is having success as an actual fanbase for owls instead of just a place for cute or silly pics.

I'm fully prepared to believe these things evolved from dinosaurs.
- Check out my latest post made just for you!
  Like the person below you said, it's pretty conclusive that they did evolve from the dinos, but much like anything, some people will still disagree for reasons.
  If you haven't seen the post about stilt-owls you are in for some fearsome owl news there too! That's one of my favorite posts.
  All birds are beautiful, but also terrifying creatures. They are fast, very strong for their size, and have a ferrocious will to survive. They will steal, kill, and do whatever it takes. Even those tiny songbirds in your feeder will raid nests and kill chicks. They'll group up to fight other birds or kill animals bigger than them. If you really watch birds, you will have no doubts that no dinosaur could be scarier than they are!
- I mean, all birds did.
- They are literally dinosaurs.
  
  It's true! This is the taxonomy of a Barn Owl:

This is amaaaazzzing! Thank you so much for all the research, clear summaries, and links. I had no idea that owls' feet were so specialized and different from other birds. I've learned a lot! Going to bookmark this keep rereading to absorb all the things.
- Awesome! I'm really glad you saw it. If you haven't scrolled all the comments, check those out too. I got to answer some good follow up questions.
  They really do have a lot of specialized body parts, plus they're super cute!
  If you come up with any other questions, just ask! I may not write another essay, but I'll answer anything the best I can.
  
  Oh nice, more goodies! Do you know offhand how it's possible for the toe to rotate? Is it not fixed in the joint as with other birds (and mammals)? Or something about where the joint attachment is located?

This was amazing and you are indeed the spiritual successor to Unidan (but don't go evil like he did; he broke our hearts).
- That was an interesting story. I was very late to Reddit, probably only being there this last 2 or 3 years.
  I don't particularly like attention, and I try to make it very clear to you guys that I am very much not an expert on anything I post, I'm just a fan that likes to learn interesting facts about things.
  I'm just hear to have fun, and when I saw those group was reformed on Lemmy but was just sitting there, it decided it was a small enough place where I could try to help.

About the picture with the owl on top of the glove: Are they fully relaxed on there - meaning, are they gripping it with full force? If so, how does the glove prevent your arm or hand from being crushed? I feel like leather would only really protect you from their talons.
- Great question! This could be a post in itself really.
  They have very fine control over there feet. Think of all the abilities you would need if your hands and feet were combined into one pair of appendages! Just like you can be relaxed overall, but make a tight fist or relax it, they can do the same.
  If you haven't looked at that Atlantic magazine link in the tendon section or the reference list, that shows how the musculature works like a pulley and lever system to increase or decrease grip. They have control over their muscles like we do, so they can regulate his hard they want to grip. They just do it the opposite way that we would, we can relax to loosen up, but they engage muscles to loosen up. I hope that makes sense.
  They also have a third leg joint so their legs are kinda Z shaped instead of > like human legs, so their geometry is very different to ours. That's why it looks funny to us to watch owls run!
  As to the gloves, their construction is to protect both the handler and the birds, so there are different construction methods for different birds.
  The leather offers some protection from the talons of course, but it also withstands more pressure and the thickness spreads the force over a wider area to learn the potential damage. Skin will rip at IIRC about 50 psi, which even the small owls can do easily, especially at the tips of the talons.
  There are bigger and thicker gloves for larger birds. They have increasing layers of leather to withstand the talons and the added pressure. Even with gloves though, I read numerous accounts of owls breaking people's fingers or making their arms go numb for a few days. A properly built and sized glove with keep the raptor feeling safe and secure so they feel the need to use less grip on the handler too.
  Here's a good article with more details and pictures!
  Raptor Glove Article
  
  Thank you for your reply! That's really interesting stuff.
  And if anyone else immediately thought about looking up running owls: here you go!

Fascinating! Excellent write-up! It was gripping (lol) from start to finish!
- It was gripping
  Perfect! 🤣

Great write up, top tier post. The feathers on the feets look like fur almost. Good stuff thanks for sharing.
- Glad you enjoyed it!
  Feathers are another potential article. There are a number of types that all serve different purposes. Owl feathers even help with their super hearing!
  
  I'd love to hear more about feathers, especially if there are some species specific features

Wow! Thank you!
- Glad you liked it! I knew it was going to be a good deal if effort to get everything collected and to find pics and all that. I try to save the real in depth things for the weekend so I have more time to work on it and to make sure more people see it after I spend the time on it.
  The main Lemmy app I use doesn't save drafts, so I had to do this one on my laptop and then get it back to my phone where I had all the pics. I've been looking into Boost which I used to use for Reddit, and that does have drafts, but some other things I don't like for making posts, so hopefully soon there will be something easier to make bigger posts with more regularly.

The bit about the toe arrangement was surprising me. Whenever I looked at bird footprints in the snow, I assumed that they were traveling in the direction of the 3 toes. Turns out, I didn't understand bird feet!
- No, you had it right, I probably just phrased it poorly.
  I had meant it as in the front toes' talons curved backwards and the rear talons faced forward.
  If we look at our bluebird friend here, you can see his 3 toes are in the front and the single in the back. Sorry if I was confusing!
- Same here

Here's channel(but in russian) about owls and some other pets.
Here are some videos.
Also there is video about owl feet.
EDIT: and hawk. Hawk and that woman work at airport chasing away other birds.
- I love that little crochet owl toy in the second video!
  Great look at the feet in the last clip.
  Eagle Owls were one of the first owls that fit be interested in them. I really like their orange eyes.
  
  She also has hawk: 1, 2, 3. They work at airport.

my toxic trait is wanting to tickle them feet
- I absolutely want to touch them. They look like a silicone kitchen scrubbee!
  
  They feel surprisingly rough, almost like snakeskin

The texture of those feet kinda scares me. It's probably nothing like I imagine though. I was already surprised by parrot and pigeon textures. I kinda imagine the owl foot bristles to be wiggly but it's probably actually sandpaper or cat tongue ish for better mouse grabbing.
I'm also curious about how an owl smells. I sniff all my birds every day.
- One other person in the comments compared it to snakeskin. I'm very curious to find out myself now. I feel it's got to have some specific texture to it since it's a survival feature for them.
  I've never given thought to hire a bird smells, but reading about the preening gland the other day, it definitely looks like something that would have some kind of smell. I've come across a few animals that get distinct smells from their scent or oil glands, so birds probably do too.
  
  My cockatiels smell like fresh paper towel rolls, my pigeon smells like down pillow washed with unscented detergent and dusted lightly with sand, one of the Senegals smells like tree resin. The rest of the birds are kinda stinky but I can't help but sniff them anyways...
  I'm slightly scared that owls might smell bad based on what they eat, but they might also not have much of a smell for stealth.

This was awesome. I learned a lot. Thank you!
- Of course! I'm glad it was a success. I've been trying to get some dialogue going on in this place, and it's been great seeing the response from everyone.

Hmm I thought of calcification of tendons as a bad thing, an evolutionary defect, or bad diet. Surprised to learn of its advantage to the owl.
- I'd like to provide a better answer, but everything I'm finding is above my level of understanding.
  From what I can decode, it seems to be of advantage to animals with specialized appendages, which I would consider raptor feet to be. The benefits for owls sound like 1) it adds strength and support to bones subject to significant and repeated shock while being lighter than actual bone, keeping energy expenditure for flight as low as possible, and 2) it prevents damage to the parts of the bone that grow new bone cells. The forces the feet get would normally kill off those cells that repair the bones.
  Human leg geometry and the jobs our legs do are very different, so while it causes pain and swelling in us, it seems to be if benefit to a number of animals.
  This article covers some various species of animals, all described as possessing specialized appendages if you want to take a shot at reading it. It seems very interesting, but these people are actual biologists, and I'm not 🤯
  Secondary ossification center induces and protects growth plate structure
  
  That's helpful. I guess it's like some in humans where parts of the skull and spine are cartilaginous at birth and ossify during adolescence. As I read your post on owls, it sounded more like degenerative ossification due to age and repetitive insult, such as in the knees of a carpetlayer or package car driver.
  Here's an image that I think shows what it's talking about. This is essentially the equivalent of the bird's finger bone. Looks like it starts off as three bones that are somewhat cartilaginous and by maturity is fused into one bone.
  https://www.researchgate.net/publication/292981174/figure/fig5/AS:391368338886658@1470320891110/Tarsometatarsus-of-basal-birds-and-its-fusion-sequence-in-living-birds-A-B.png

This is top tier content. Thanks for sharing.
- I'm just so glad it's a hit! I spent a few hours on it and I was so worried only a few people would be interested.

So do you think it was an owl or did Michael Peterson push his wife down the stairs?
- I hadn't heard of this, I'll have to check it out!
- So I didn't read about the case itself, but I did read 2 things about "The Owl Theory."
  I was going to say it was a bit far fetched at first, but I saw the Barred Owl I posted about in Boston the other week is still attacking people there, and there is not stage of photos of owl talon damage to people of you Google that.
  The owl feather material in her hair seems hard to come by any other way, but I would think they could ID the cuts in autopsy of I could find pictures of owl talon cuts. That may just be CSI Miami overestimating real abilities though...
  I'd also think they'd be able to locate the owl, or at least signs of the owl like pellets. Barred Owls are territorial because they don't migrate and have a pretty small home territory.
  Thank you for mentioning this case though, it was very interesting to read about!

i wonder if arm wrestlers can keep up with the owls grip strength. like arm wrestlers mostly train grip strength. my guess is that professional arm wrestlers could reach 400psi
- After skimming some arm wrestling and grip strength from posts, it looks like 300 pounds on a hand Dyno will put you in legend territory, but I don't know if that's straight pounds or psi it's measuring, so I can't say it's apples to apples.
  Those guys weigh a bit more than a 3 pound owl though, so either way the owl is very impressive!
  
  yeah, obviously. that was never a question. i just wondered if a human could reach that strength regardless of strength to weight ratio
- I think that everyone is misunderstanding pressure and what psi (pounds per square inch) is measuring. This is force applied over a surface area. There are two ways to increase pressure: 1. Increase the force 2. Decrease the surface area.
  I assume that 500 PSI is being measured at the very pointy tips of the Owl's talons. This demonstrates their ability to pierce and grab their prey but it is misleading.
  I can easily generate 5000 PSI by stabbing with a sharp knife. That is not the same thing as what everyone is thinking of as "grip strength" which is like closing the Captains of Crush grip trainers. There is no way an owl could close the No. 4 CoC (365 lb) note this isn't 365 PSI, this is 365 lb. Meaning you can generate 365 lb of force with your closing grip. If you could apply that force to a talon that came to a point of .001 square inches, you would generate 365,000 PSI
  
  true. forgot about that. psi is unknown to me but bar or pascal is
  
  Thank you for this, I couldn't find much on the exact testing method used.

82 comments